Synthesis and cytotoxic evaluation of substituted 3-(3′-indolyl-/3′-pyridyl)-isoxazolidines and bis-indoles

Regio- and stereoselective 1,3-dipolar cycloadditions of C-(3-indolyl)-N-phenylnitrone (10) were carried out with different mono-substituted, disubstituted and cyclic dipolarophiles under mono-mode microwave irradiation to obtain substituted 3-(indol-3′-yl)-N-phenyl-isoxazolidines (16–22). Reactions of nitrone (10) with allenic esters under similar conditions afforded, via a domino process, bis-indole derivatives (23a–c) along with compounds 24 and 25. Similarly, reactions of C-(3-pyridyl)-N-phenylnitrone (26) with mono-substituted, disubstituted and cyclic dipolarophiles were carried out in refluxing dry toluene to obtain substituted 3-(3′-pyridyl)-N-phenylisoxazolidines (27–34). Some of the compounds (16f, 18b, 23a, 23c, 27c and 29f) display significant cytotoxicity against a number of human cancer cell lines.